1. Field of the Invention
The present invention relates to a method of transmitting feedback information, and more particularly, to a method of transmitting feedback information in an Orthogonal Frequency Division Multiplexing (OFDM)/OFDM Access (OFDMA) mobile communication system.
2. Discussion of the Related Art
In a multi-input, multi-output (MIMO) wireless communication system employing an Orthogonal Frequency Division Multiplexing (OFDM) method, feedback information is transmitted from a mobile station (MS) to a base station (BS). The OFDM method uses a plurality of subcarriers to increase the frequency usage rate. Here, the subcarriers maintain orthogonal relationships with each other.
In operation, the BS allocates a fast feedback channel in order to acquire downlink channel status information, and using the fast feedback channel, the BS transmits a Channel Quality Information Channel (CQICH) Information Element (IE) or put differently, a CQICH_enhanced_allocation IE. At the same time, the BS uses a subheader (or fast feedback_allocation subheader) to allocate the CQI channel.
In the MIMO system, the feedback information is transmitted via the allocated CQICH or the fast feedback channel. The feedback information includes the MIMO channel matrix H and the weight value, along with information pertaining to MS selected MIMO mode and MS selected permutation mode. Here, the MIMO mode includes a Space-Time Transmit Diversity (STTD) mode, a Spatial Multiplexing (SM) mode, and a closed loop SM mode, for example. Moreover, the permutation mode includes a Full Usage Subcarrier (FUSC), which uses all the subcarriers in the bandwidth to achieve diversity, a Partial Usage Subcarrier (PUSC), which uses a specified amount of subcarriers to achieve diversity, and an Adoptive Modulation Coding (AMC), which uses a specified amount of subcarriers adjacent to each other.
According to the related art, the MS transmits the feedback information according to the instruction provided from the BS. However, even if the MS desires to transmit feedback information to the BS, the MS has to wait until the BS transmits instruction to do so. As such, the transmission channel is not effectively or efficiently utilized.